This invention relates to thermoplastic film, and more particularly a thermoplastic film which provides a high oxygen barrier. More particularly, this invention relates to a thermoplastic composite film which provides a high oxygen barrier.
It is well known that ethylene vinyl alcohol copolymers (EVOH) may act as an oxygen barrier in multilayer films. It is also known that vinylidene chloride copolymer, commonly known as saran, may also exhibit oxygen barrier characteristics in a multilayer film. However, the characteristics of these barrier agents are such that their effectiveness as oxygen barriers is affected by the humidity of the environment in which the film is used, i.e., the barrier properties of these barrier agents are humidity sensitive.
The article Ethylene Vinyl Alcohol Resins for Gas-Barrier Material by T. Iwanami and Y. Hirai discusses the humidity dependence of ethylene vinyl alcohol in estimating its gas-barrier properties. Ethylene vinyl alcohol has good gas-barrier properties, including oxygen barrier properties in low-humidity conditions, but these properties degrade at high humidity. It is known to coat polyvinyl alcohol with for example saran, and to construct a multilayer film in which a core layer of ethylene vinyl alcohol is sandwiched between layers including for example a saran-coated web and heat-sealant layer.
It is, therefore, an object of the present invention to provide a thermoplastic film in which high oxygen barrier characteristics are obtained.
It is a further object of the invention to provide a thermoplastic film in which high oxygen barrier characteristics are obtained over a wide range of humidity conditions.
It is a further object of the present invention to provide a thermoplastic composite film in which high oxygen barrier characteristics are obtained.
It is a further object of the present invention to provide a thermoplastic composite film in which high oxygen barrier characteristics are obtained over a wide range of humidity conditions.
It is a further object of the present invention to provide a thermoplastic composite film in which high oxygen barrier characteristics are obtained over a wide range of humidity conditions, the composite film being formed from four individual films which are bonded to each other by corona bonding.